Methods for forming openings in a substrate and apparatuses with these openings and methods for creating assemblies with openings

ABSTRACT

Methods for forming openings having predetermined shapes in a substrate and apparatuses with these openings. The methods may be used to form assemblies which include the substrate with its openings and elements which are disposed in the openings. In one example of a method, each of the elements include an electrical component and are assembled into one of the openings by a fluidic self assembly process. In an particular example of a method to create such an opening, the substrate is etched through a first patterned mask and is later etched through a second patterned mask. Typically, the second patterned mask is aligned relative to the opening created by etching through the first patterned mask and has an area of exposure which is smaller than an area of exposure through the first patterned mask. In another example of a method, a photosensitive material is exposed through a patterned mask to oblique sources of light such that some of the light impinges into a first portion of the photosensitive material which is under the patterned mask, and the patterned mask and a second portion of the photosensitive material, which is under the patterned mask, is removed. In another example of a method, an opening in a first layer, which comprises silicon dioxide, is formed by depositing a second layer over the first layer and depositing a tungsten layer over the second layer. The tungsten and second layers are patterned to expose a portion of the first layer, and this portion is etched. Various apparatuses which may be made using these methods are also described.

RELATED APPLICATIONS

This application is a divisional of co-pending U.S. patent applicationSer. No. 10/154,899, filed May 23, 2002 which is a divisionalapplication of U.S. patent application Ser. No. 09/432,512, filed onNov. 2, 1999 entitled “Method and Apparatus for Forming Openings in ASubstrate and Apparatuses with these Openings and Methods for CreatingAssemblies With Openings” and now issued as U.S. Pat. No. 6,479,395.

GOVERNMENT RIGHTS NOTICE

This invention was made with government support with at least one ofthese contracts: Grant (Contract) Nos. AFOSR 91-0327; F49620-92-J-059-1;F33615-96-C-5111 with USAF/AFMC/ASC; DAA016-00-C-9234 USAMCAC (US Army);Northrop Grumman PO #8200014995 (subcontract, NOOO14-99-C-0395 (prime));North Dakota State University Subcontract #4080, DMEA 90-01-C-0009(prime) and University of Alaska, Fairbanks PO#FP201509 (subcontract),DMEA 90-01-C-0009 (prime). The Government has certain rights to thisinvention.

FIELD OF THE INVENTION

The present invention relates generally to the field of fabricatingopenings in a substrate and also to apparatuses with these openings.More particularly, the present invention relates to methods for formingopenings in a substrate which openings are designed to receive anelement which is later placed into the opening and which elementincludes at least one functional component, and the present inventionrelates to methods for creating assemblies with the openings.

BACKGROUND OF THE INVENTION

There are many examples of large arrays of functional components whichcan provide, produce or detect electromagnetic signals or chemicals orother characteristics. An example of such a large array is that of adisplay where many pixels or sub-pixels are formed on an array ofelectronic elements. For example, an active matrix liquid crystaldisplay includes an array of many pixels or sub-pixels which arefabricated on amorphous silicon or polysilicon substrates which arelarge. As is well known in the art, it is difficult to produce acompletely flawless active matrix liquid crystal display (LCD), when thedisplay area is large, such as the LCD's on modem laptop computers. Asthe display area gets larger and larger, the yield of good displaysdecreases. This is due to the manner in which these display devices arefabricated.

Silicon VLSI can be used to produce such an array over a silicon wafer'ssurface, but silicon wafers are limited in size, limited inconductivity, and not transparent. Further, processing of large areas onsilicon wafers can be expensive. Displays which valve the light comingthrough them need to be transparent. Single crystal silicon can bebonded to a glass substrate and then etched to remove most of the areato achieve transparency, but this is intrinsically wasteful in that, forthe sake of maximizing light transmission, the majority of the processedmaterial is discarded and becomes chemical waste. The under-utilizationof the precious die area wastes resources, causes greater amounts ofchemical waste to be generated in the process, and is generallyinefficient and expensive. Another example is photodiode arrays whichmay be used to collect solar energy. Large arrays of silicon photodiodeswith concentrating lenses have been made by sawing wafers and using apick and place assembly, but thermal dissipation is poor for largeelements, and the small elements require too much assembly time.

Alternative approaches to fabricating arrays such as displays includefabricating the desired circuitry in an amorphous or polycrystallinesemiconductor layer which has been deposited on a substrate, such asglass or quartz. These approaches avoid the limitations of the size ofthe available single crystal silicon wafers, and avoid the cost of thesingle crystal wafers, but require expensive deposition of thesemiconductor layer, and they still require processing of the entirelarge substrate to form the active elements in an array, still resultingin the production of much chemical waste and wasted resources. Theseprocesses also limit the choice of the substrate; for example, plasticsubstrates cannot be used due to the nature of the processes whichdeposit the semiconductor layers. Furthermore, amorphous orpolycrystalline silicon semiconductor elements do not perform as well asthose made from single crystal semiconductor material. For displays, asan example, it is often difficult or impossible to form some of thedesired circuitry out of the amorphous or polycrystalline semiconductormaterials. Thus, high frequency edge drivers may be impossible to formout of these materials. This results in the difficulty and expense ofattaching an electrical lead for each and every row and column of anarray, such as an active matrix liquid crystal display array.

As noted above, another difficulty with the existing techniques is thatthe large number of elements in a large array results in a lowprobability that all of them will work properly and thus the yield ofacceptably good arrays from the manufacturing process is low.Furthermore, there is no possibility of testing any of the elementsuntil the assembly is complete, and then any imperfection in the arraymust be tolerated or the entire array could be discarded or special andexpensive techniques must be used to repair it. These problems resultfrom the fact that the various elements in the array are fabricated onthe array rather than separately.

It is possible to separately produce elements, such as pixel drivers andthen place them where desired on a different and perhaps largersubstrate. Prior techniques can be generally divided into two types:deterministic methods or random methods. Deterministic methods, such aspick and place, use a human or robot arm to pick each element and placeit into its corresponding location in a different substrate. Pick andplace methods place devices generally one at a time, and are generallynot applicable to very small or numerous elements such as those neededfor large arrays, such as an active matrix liquid crystal display.Random placement techniques are more effective and result in high yieldsif the elements to be placed have the right shape. U.S. Pat. No.5,545,291 describes a method which uses random placement. In thismethod, microstructures are assembled onto a different substrate throughfluid transport. This is sometimes referred to as fluidic self assembly(FSA). Using this technique, various blocks, each containing afunctional component, may be fabricated on one substrate and thenseparated from that substrate and assembled onto a separate substratethrough the fluidic self assembly process. The process involvescombining the blocks with a fluid and dispensing the fluid and blocksover the surface of a receiving substrate which has receptor regions(e.g. openings). The blocks flow in the fluid over the surface andrandomly align onto receptor regions.

Thus the process which uses fluidic self assembly typically requiresforming openings in a substrate in order to receive the elements orblocks. Methods are known in the prior art for forming such openings andare described in U.S. Pat. No. 5,545,291. One issue in forming anopening is to create its sidewalls so that blocks will self-align intothe opening and drop into the opening. The substrate having openings inthe glass layer 10 may be used as a receiving substrate to receive aplurality of elements by using a fluidic self assembly method. FIG. 1Ashows an example where a separately fabricated element 16 has properlyassembled into the opening 14. However, it has been discovered that attimes, an element 16 will not properly assemble into an opening 14 dueto the fact that the element 16 becomes turned upside down and thenlodges in the top of the opening 14. An example of this situation isshown in FIG. 1B. Often times, the inverted element 16 lodges into theopening 14 so tightly that it remains in the opening and preventsnon-inverted elements from falling into the opening 14. Thus, theopening at the end of the assembly process will typically not be filledwith an element or perhaps worse, may still contain an inverted elementlodged at the top of the opening 14.

FIGS. 2A through 2D show an example in the prior art for creating aplurality of openings in a receiving substrate which is designed toreceive a plurality of separately fabricated elements which aredeposited into the openings through fluidic self assembly. The methodshown in FIGS. 2A through 2D begins by, in one example, thermallygrowing a silicon dioxide layer on a silicon substrate 20. The resultingstructure is shown in FIG. 2A with the silicon dioxide layer disposedover the silicon substrate 20. Then, a photoresist material may beapplied, and exposed through a lithographic mask and then developed toproduce a patterned mask formed from the developed photoresist. Then anetching solution is applied to etch through the patterned mask to createan opening 24 in the silicon dioxide layer 22. The resulting structureis shown in FIG. 2B. Then, the silicon dioxide layer 22 with its opening24 is then used as a patterned mask to etch the silicon layer 22 tocreate the opening 26 in the silicon layer 20 as shown in FIG. 2C. Thisetching of the silicon layer 20 may be performed with a KOH etchant orwith an EDP etchant as described in U.S. Pat. No. 5,545,291. Afteretching the opening 26 in the silicon layer 20, the silicon dioxidelayer 22 is removed, for example, by an etch in a hydrofluoric acidsolution. This results in the structure shown in FIG. 2D where theopening 26 is now ready to receive a separately fabricated elementthrough an assembly process, such as for example, fluidic self assemblyor perhaps a pick and place procedure. The structure shown in FIG. 2Dhas the drawback that a monocrystalline silicon layer is required inorder to use the KOH etch to form the hole.

Often, it will be desirable to obtain a deep enough opening withoutmaking the opening too wide. This, of course, will depend on the shape,which is typically predetermined, of the separately fabricated elementor block which is to be deposited into the opening. Naturally, the shapeof the opening is designed to fit substantially the shape of theseparately fabricated element. Often times, it is necessary to obtain anangle in the opening which is steeper than a 45° angle. These variousrequirements and the problems associated with inverted elements whichbecome lodged in openings have resulted in attempts to improve themethods for fabricating the openings in a receiving substrate.

From the above, it is seen that it is desirable to provide methods forforming openings in a receiving substrate and to provide methods forcreating assemblies with these openings.

SUMMARY OF THE INVENTION

The present invention provides various methods for creating an openingin a substrate and also provides apparatuses resulting from thesemethods. In one example of a method according to the present invention,an opening which has a predetermined cross-sectional shape is created ina substrate. The opening is designed to receive an element which isseparately fabricated and which typically includes at least onefunctional component and which is placed into the opening in a processsuch as pick and place or fluidic self assembly. In this example, themethod involves etching the substrate through a first patterned mask fora first portion of an etch time and etching the substrate through asecond patterned mask for a second portion of the etch time. In oneparticular example of this method, the first and second patterned masksare different.

In another example of a method according to the present invention, anopening which has a predetermined cross-sectional shape in a substrateand which is designed to receive an element which is placed into theopening is created by applying a patterned mask over a material which issensitive to electromagnetic radiation and exposing the material and thepatterned mask to electromagnetic radiation which is project obliquelyto a surface of the material such that some of the electromagneticradiation impinges into a first portion of the material which is underthe patterned mask. The patterned mask is removed and a second portionof the material which was under the patterned mask is also removed.

According to another aspect of the present invention, a method isprovided for forming an opening in a first layer which includes silicondioxide. In this method, a second layer is deposited over the firstlayer which includes silicon dioxide, and a metal adhesion layer, suchas a tungsten layer is deposited over the second layer. The metaladhesion layer is patterned and the second is patterned to expose aportion of the first layer which is then etched.

The present invention also provides a substrate having at least oneopening which is designed to receive an element having a predeterminedshape. The element is fabricated separately and assembled into theopening. The opening includes in a region near its top edge a beveledsurface which in one exemplary embodiment is designed to decrease thefrequency of inverted elements from being wedged into the top of theopening.

According to another aspect of the invention, a method for creating anopening in a layer is described. The opening is for receiving an elementwhich is placed into the opening. The method includes forming a firstlayer on a substrate, depositing a second layer over the first layer,and ablating selectively the second layer at at least one desired regionto create an opening in the second layer at the at least one desiredregion, wherein the ablating stops automatically at the first layer.

According to another aspect of the invention, another method forcreating an opening in a substrate is described. The opening is forreceiving an element which is fabricated on another substrate and isplaced in the opening. The method includes forming an organic layer on aglass substrate and forming an opening in the organic layer.

According to another aspect of the invention, a method for etching glassin an etching solution is described. The etching solution has certaindescribed concentrations of hydrofluoric acid, a counter acid (e.g. HCl,HBr, HI, HNO₃, or H₂SO₄) and water and the etching of the glass with theetching solution is performed at a reduced temperature in the range ofabout 0° C. to about 10° C.

These aspects as well as other features of the present invention will bedescribed further below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example and notlimitation in the figures of the accompanying drawings in which likereferences indicate similar elements.

FIGS. 1A and 1B show examples of how a block can mate with an opening ina receiving substrate, which opening is designed to receive a separatelyfabricated element which includes at least one functional component.

FIGS. 2A through 2D show another method in the prior art for formingopenings in a receiving substrate.

FIGS. 3A through 3G show cross-sectional views of one method accordingto the present invention of forming an opening in a receiving substrate,and FIG. 3H is a perspective electron micrograph image of an openingformed according to this method.

FIG. 3I shows an example of a block in a hole.

FIGS. 4A through 4F show in cross sectional views another methodaccording to the present invention for forming openings in a receivingsubstrate.

FIGS. 5A through 5F show in cross sectional views another methodaccording to the present invention of forming openings in a receivingsubstrate.

FIGS. 6A through 6F illustrate in cross sectional views another exampleof the present invention for forming openings in a receiving substrate.

FIGS. 7A through 7E show in cross sectional views another methodaccording to the present invention for forming openings in a receivingsubstrate.

FIGS. 8A through 8F show another method for forming openings in areceiving substrate according to the present invention. FIGS. 8A, 8B,8D, 8E, and 8F are cross sectional views, and FIG. 8C is a top planview.

FIG. 9A is a flowchart which illustrates a general process for formingan assembly by placing elements into the openings in the receivingsubstrate.

FIGS. 9B, 9C and 9D show a cross-sectional view of one example of anassembly according to the present invention in which silicon blockswhich include electrical functional components are assembled into theopenings in a receiving substrate which in this case is a glasssubstrate.

FIGS. 9E, 9F, 9G, and 9H show cross-sectional views of another exampleof an assembly according to the present invention in which siliconblocks, which include functional components, are assembled into theopenings in a receiving substrate. The openings shown in FIGS. 9E, 9F,9G and 9H may be formed with the method illustrated in FIGS. 3A-3G.

FIG. 9I is a perspective electron micrograph image of a silicon blockwhich has been placed into an opening in a substrate, and electricalinterconnects have been formed to the silicon block.

FIG. 10 shows a flowchart which indicates a method for creating anassembly of blocks and a receiving substrate which receives the blocksinto openings on the receiving substrate.

FIGS. 11A and 11B show two examples of nozzles which may be used todispense a slurry of blocks onto a receiving substrate.

FIGS. 12A and 12B are cross-sectional views of a substrate in which anopening is created according to another method of the present invention.

FIGS. 13A and 13B are cross-sectional views of a substrate in which anopening is created according to another method of the present invention.

DETAILED DESCRIPTION

The present invention relates to methods and apparatuses for formingopenings in a receiving substrate. The following description anddrawings are illustrative of the invention and are not to be construedas limiting the invention. Numerous specific details are described toprovide a thorough understanding of the present invention. However, incertain instances, well known or conventional details are not describedin order to not unnecessarily obscure the present invention in detail.

The present invention relates generally to the field of creatingopenings in a receiving substrate and to apparatuses having theseopenings. The present invention may be used to fabricate openings forvarious different types of arrays. Typically, each element in the arrayincludes a functional component which may be an electrical component, achemical component, or an electromechanical structural element or amicro electromechanical structural element or a micro-mechanicalstructural element. The various methods of the present invention areillustrated in certain detailed examples with regard to the manufactureof an active matrix liquid crystal display, but it will be recognizedthat the invention will have wider applicability. Merely by way ofexample, the invention may be applied to the fabrication of anelectronic array which can be used to deliver precise voltages for thecontrol of liquid crystal cells to create a liquid crystal display ormay be used for other types of displays such as electro-luminescentdisplays or light emitting diode displays or displays usingelectrophoretic ink display pixels, such as microencapsulatedelectrophoretic ink display pixels, and also for other applicationsrequiring sampling or producing electrical signals over a large array ofelectrodes, such as memories and imaging arrays and photo diode arrays.Further, the present invention may be used with electromagnetic signaldetectors (e.g. antennas), or solar cells, or chemical sensors.

In a preferred embodiment of the present invention, an opening has apredetermined size which is designed to receive an element also of thesame predetermined size so that the element fits into the opening. Bycontrolling the fit between the element and the opening, it is possibleto have the elements self assemble into the openings. Accordingly, in apreferred embodiment of the present invention, each element has atrapezoidal cross-sectional shape which fits into a trapezoidal openingin which the top of the opening has a larger area than the bottom of theopening. Furthermore, it is desirable to form a deep opening withoutmaking the opening too wide. FIGS. 3A through 3G illustratecross-sectional views after various processing operations according toone example of the present invention.

The method shown by FIGS. 3A through 3G begins with the substrate 101which is typically glass in the case of an active matrix liquid crystaldisplay (of the transmissive type). It will be appreciated that thissubstrate may be a different material for other types of arrays. Theglass substrate 101 is covered by an amorphous silicon layer 102 whichmay be deposited by PECVD to a total thickness of approximately 500Angstroms to three thousand Angstroms. An optional tungsten layer 103(or other metal adhesion layers such as, for example, titanium,tungsten, or chrome) may be deposited by sputtering; this optionaltungsten layer 103 is deposited on top of the amorphous silicon layer102 as shown in FIG. 3A. Then lithography is used to provide a patternedmask layer with openings of the shape desired for the resulting hole inthe substrate 101. In one case, the size of the openings in thesubstrate are approximately 0.5 microns to 5 microns larger than theblocks to be assembled into the openings. Typically, a photoresist isused to create the patterned mask. This patterned mask may be created ontop of the optional tungsten layer 103 by spinning photoresist onto theentire structure, exposing the photoresist through a lithographic maskand then developing the photoresist layer to create the pattern mask.Then the tungsten layer 103 is etched and the amorphous silicon layer102 is etched to creating an opening 104 as shown in FIG. 3B. Theoptional tungsten layer is used to increase adhesion to photoresist toprevent pinholes in the underlying structure and results in an improvedreceiving substrate. This opening 104 exposes the top surface of thesubstrate 102 so that it may be etched to create the opening 105 shownin FIG. 3C.

In one example of the present invention, the etch to create the opening105 is a wet etch. The preferred etch mix depends on the type of glassused. The etch mix contains dilute hydrofluoric acid and, preferably, anadditional acid such as nitric acid, sulfuric acid, perchloric acid, ormore preferably a halide acid such as hydrobromic acid or hydrochloricacid or hydriodic acid. The ratio of water to the second acid tohydrofluoric acid ranges from 2:1:1 to 50:20:1, depending on the type ofglass used for the substrate. The substrate is etched for roughly onequarter of the total etch time. In one particular embodiment, the ratiosof an etchant which includes water, hydrochloric acid and hydrofluoricacid is 4:1:1 (water:hydrochloric:hydrofluoric) and the total etch timeis such that the total depth of the etchant produces an opening having adepth of 14.5 microns.

The glass can be etched with any hydrofluoric acid-based etch solution,with hydrofluoric acid concentration ranging from concentratedhydrofluoric acid to 1% concentrated hydrofluoric acid in water. In apreferred embodiment, the glass is soda lime glass, and is etched with amixture of hydrofluoric acid:counter acid:water in which the watercontent ranges from 50% to 95%, the hydrofluoric acid content rangesfrom 25% to 1%, and the counter acid content ranges from 40% to 5%. Thecounter acid could be nitric acid or sulfuric acid, or more preferably,hydriodic acid, or hydrobromic acid, or most preferably, hydrochloricacid. The temperature of the etching solution is maintained at atemperature in the range of from −10° C. to 40° C. In a more preferredembodiment, the glass is borosilicate or aluminosilicate glass, such asComing 7059 or Coming 1737, respectively, and is etched in an etch mixas above, in which the water content ranges from 60% to 95%, thehydrofluoric acid content ranges from 10% to 1%, and the counter acid,as described above, ranges from 30% to 5%. In the most preferredembodiment, the temperature of the borosilicate or aluminosilicate glassetch described above is controlled to within 0.5 degrees C., at aspecified temperature between −5 and 5 degrees C. In the most preferredembodiment, the etch solution is 1 part HF to 10 parts HCl to 100 partsH₂O.

After the opening 105 has been formed in the substrate 101 as shown inFIG. 3C, the tungsten layer 103 and the amorphous silicon layer 102 areremoved over the entire substrate, and then the entire substrate isblanket etched for an additional one quarter of the entire etch time.This produces the structure shown in the cross-sectional view of FIG. 3Din which the opening 105 is deepened and at the same time the top edgeof the opening is widened to provide the beveled edge 106 which iscreated by the removal of material from the top of the substrate andsides of the hole, thereby changing the shape of the sides of the hole.Typically, this blanket etch is the same etch mix used to create theinitial opening 105 shown in FIG. 3C. The beveled edge 106 at the top ofthe opening 105 tends to prevent an inverted element from lodging at thetop of the opening 105 during the assembly of the element into theopening. As can be seen from FIG. 3G, the beveled edge 106 creates anopening which has at least two slopes along the surface of the opening,where one of these slopes is an average of the slopes along the edge 106and the other slope is substantially vertical as shown in FIG. 3G.

After the beveled edge is created at the top of the opening, anotheramorphous silicon layer 108 is deposited onto the entire top of thesubstrate. The amorphous silicon may be deposited by a PECVD or CVD or asputtering process to a total thickness of about a thousand Angstroms.An optional tungsten layer (which is preferably about 100 to 1000Angstroms thick) may then be deposited (e.g. by sputtering) on the layer108. Then a photoresist layer 109 is applied to the top of the amorphoussilicon layer 108 (or on top of the optional tungsten layer if thetungsten layer is applied), and this photoresist layer 109 is patternedto create the opening 110 in the photoresist layer 109 (and in theoptional tungsten layer if present) as shown in FIG. 3E. The patternedphotoresist layer 109 forms an opening 110 which is smaller than theoriginal opening 104 in the patterned mask used to create the structureshown in FIG. 3B. The exposed surface of the amorphous silicon layer108, which is exposed at the opening 110 as shown in FIG. 3E, is thenetched to create an opening 111 as shown in FIG. 3F. This opening 111exposes a top surface of the substrate 101 which is at the bottom of theopening 105 as it now exists in this sequence of processing operations.The substrate 101 is now etched through the opening 111 with the sameetch solution described above to create the opening shown in FIG. 3G.FIG. 3G shows the opening after the amorphous silicon layer 108 and thephotoresist layer 109 have been removed. Typically, the patternedphotoresist layer 109 is first stripped (and if present the optionaltungsten layer is stripped) and then the amorphous silicon 108 isremoved creating the structure shown in FIG. 3G.

FIG. 3H shows an electron micrograph image of an opening which may beformed with the method shown in FIGS. 3A-3G. FIG. 9E is across-sectional view of a similar opening. As can be seen from FIG. 3Hand FIG. 9E, the opening has a bevel at its top edge. The rest of theopening is deep without having an upper cross-sectional area which istoo large. If this upper cross-sectional area of the opening is toolarge, then inverted blocks will tend to get stuck in the opening. FIG.3I is a stick drawing of a block in an opening. The edge 115A of theopening nearly abuts the edges 115B and 115D of the top of the block.The bottom edge 115C of the block is shown through the body of the blockwhich has been made, for purposes of illustration, to be transparent. Anexample of dimensions for a particular block and matching opening willnow be provided.

By means of an example, given a block 353 with the cross-section shapeshown in FIG. 9F and dimensions: bottom width 131 microns, top width 182microns and total thickness of 38 microns, circuit thickness 2 micronsand angles of 54.7 degrees. The suitable hole would be etched with thefollowing parameters. Opening 104 in layers 103 and 102 of FIG. 3Bshould be of width 145 microns. Then the glass should be etched (seepreviously mentioned etch conditions) a total of 14 microns. This formsopening 105 in the glass with a total width of 173 microns. Then theblanket etch (between 3C and 3D) should be for a depth of 7 microns.This increases the opening 105 to a width of 185 microns. The opening inthe second mask material (108 of 3F) should be of a width 130 microns.The glass should then be etched a total of 24 microns making the depthof the hole 38 microns. The cross-section of the block 353 and hole 351combination is shown in FIG. 9F.

The following parameters create a block and opening combination whichproduces good self-assembly. Block Parameters Hole Parameters thickness= 38.0—38.0 depth = 38.0—38.0 top1 = 184.6—184.6 bottom_width = etch1 =14.0—14.0 top2 = 173.0—173.0 131.0—131.0 Top_width = etch2 = 7.0—7.0length1 = 145.0—145.0 181.9—181.9 delta_thickness = 2.0 etch3 =24.0—24.0 length2 = 130.0—130.0 delta_corner = 10.0 marker = 19.8radius1 = 4.0 radius2 = 12.0

In one example of the method shown in FIGS. 3A through 3G, the totaldepth of the opening is 39 microns, and three etches are used to createthe opening, where the total etch time is the total time for the threeetches. The first and the third etch are through a first and secondpatterned mask respectively, and the second etch is without a patternedmask or at least uses a mask which allows the top edge of the openingsto be exposed. Typically, the first etch is for a quarter of the totaletch time, the second etch is for a quarter of the total etch time, andthe third and last etch is for one half of the entire etch time. Usingthe method shown in FIGS. 3A through 3G, it is possible to create a deepopening which is not too wide and which includes a beveled edge. Thisopening has improved characteristics for receiving separately fabricatedelements which may be assembled by a self assembly process, such asfluidic self assembly.

FIGS. 4A through 4F show cross-sectional views through an openingfabricated according to another method of the present invention. Each ofthese figures shows the state of the opening after certain other processoperations in this method. FIG. 4A shows a patterned mask layer 132which includes an opening 133 exposing a top surface of a substrate 131which may be glass in one embodiment. The patterned mask layer 132 maybe, for example, chrome. The exposed areas of the substrate 131 areetched using an appropriate etchant. In one example, this etch is a wetetch bath using hydrofluoric acid which creates the opening 134 in thesubstrate 131 as shown in FIG. 4B. This etch in one example istwo-thirds of the total etch time used in the process shown in FIGS. 4Athrough 4F. A second blanket mask, such as a photoresist layer, isdeposited over the entire substrate. FIG. 4C shows an example when theblanket mask layer 135 has been deposited over the entire substrate andhas filled the opening 134. This second blanket mask layer is thenpatterned using, for example, photolithography, to pattern thephotoresist layer 135 to create the opening 136 shown in FIG. 4D. Thisopening exposes the bottom surface of the opening 134 in the substrate131. The size of the opening 136 is smaller than the size of the opening134 as can be seen by comparing FIGS. 4B and 4D. The substrate shown inFIG. 4D is then etched again to etch the exposed surfaces of thesubstrate through the openings 136 to create the opening 137 shown inFIG. 4E. Then the patterned photoresist layer 135 is removed by aconventional stripping operation and the chrome layer 132 is removedresulting in the structure shown in FIG. 4F in which the substrate 131now includes an opening which has a staircased or beveled edge as shownin FIG. 4F.

It will be appreciated for the process shown in FIGS. 4A through 4F, theetchant used to etch the substrate will depend upon the material of thesubstrate, and the masking layers will be designed to be resistant tothose etchants. Typically, the second mask material, such as thephotoresist layer 135 is patterned with a vertical etch. In oneembodiment, the same lithographic mask which created the patterned layer132 may be used to create the pattern in the photoresist layer 135(although this is not shown in FIGS. 4B and 4D). The etch which createsthe opening 137 may be a wet chemical etch (such as an etchantcontaining hydrofluoric acid) which is approximately two-thirds of thetotal etch time when the first etch to create the opening 134 was forone-third of the total etch time.

FIGS. 5A through 5F show another example of a method according to thepresent invention. The cross-sectional views through the substrate 151shown in FIGS. 5A through 5F illustrate the structure of an opening asit is created using this exemplary method. It will be appreciated that aplurality of such openings are formed in the substrate 151 which may bean array of openings designed to receive separately fabricated elementswhich are assembled into the opening in subsequent processing. This isalso true for the opening which is created using the other examples ofmethods of the present invention. FIG. 5A shows that a top region of thesubstrate 151 is exposed by an opening 152 in the patterned mask layer153. In one embodiment, this patterned mask layer may be chrome oramorphous silicon formed by PECVD or CVD or sputtered amorphous silicon.The opening 152 is created using standard lithography techniques. Thisopening matches the shape of the desired hole. The substrate with thepatterned mask 153 is then placed in a wet etch bath to create theopening 154. In one exemplary embodiment, a hydrofluoric acid etchetches the substrate 151 in its exposed regions to create the opening154 as shown in FIG. 5B. In one example, this etch is for two-thirds ofthe total etch time, which total etch time includes the etching throughthe opening 157 to create the opening 158 as shown in FIGS. 5D and 5E.

After the opening 154 is created, a second mask material 155 is appliedover the substrate 151 and into the hole 154 after the patterned masklayer 153 has been removed. This results in the structure shown in FIG.5C. Then the second mask material 155 is patterned to create the opening157, typically using a vertical illumination. This results in thestructure shown in FIG. 5D in which the opening 157 exposes a bottomportion of the opening 154 as shown in FIG. 5D. Then another etch isperformed through the opening 157 to create the opening 158 shown inFIG. 5E. In one particular embodiment, a hydrofluoric acid etch forone-third of the total etch is used to create the opening 158. Then thepatterned mask material layer 155 is removed, which results in thestructure shown in FIG. 5F. As can be seen from FIG. 5F, the opening 158includes a beveled edge or a stairstep edge which provides for improvedsettling of elements into the hole and prevents lodging of invertedelements.

Another example of a method according to the present invention will nowbe described in conjunction with FIGS. 6A through 6F. A first maskmaterial is applied on top of the substrate 201, and this first maskmaterial is then patterned to create the first patterned mask 202 asshown in FIG. 6A. Then the substrate 201 is exposed to an etchant, whichis typically a wet etch, which creates the opening 201A as shown in FIG.6B. Then the patterned first mask layer 202 is removed and aphoto-polymerizable layer 203 is applied over the entire substrate,filling the holes as shown in FIG. 6C. A second mask material is appliedover the photo-polymerizable material 203, and this second mask materialis patterned to create the opaque mask 204 which is shown aligned overthe central region of the opening 201A. This can be seen from FIG. 6D.Also as shown in FIG. 6D, the opaque mask 204 is used to mask obliquelydirected light 205 and 206 as shown in FIG. 6D. The obliquely directedlight, obliquely directed from both sides of the opening as shown inFIG. 6D causes the light to pass partly under the mask 204. Because themask 204 is opaque, some of the region under the mask 204 will not beexposed and another portion near the edges of the mask 204 will beexposed. It will be appreciated that four sources of light obliquelyangled relative to the top surface 203 will typically be necessary inorder to create an opening having four sides. The light will polymerizethe photo-polymerizable material in all places where the material isexposed. Thus, the material which remained unexposed under the mask 204will be etched away resulting in the opening 208 shown in FIG. 6E. Thevarious materials and etchants which may be used will be apparent tothose skilled in the art. For example, a photo-polymerizable polyimidemay be used. The opening 208 forms a patterned layer 203 which exposes aportion of the bottom of the opening 201A as shown in FIG. 6E. Thisopening is then etched with an etchant, such as an etchant containinghydrofluoric acid when the substrate 201 is a glass. This etch processcreates the opening 209 as shown in FIG. 6F.

FIGS. 7A through 7D show an alternative embodiment in which thesubstrate 201 is not etched but the photo-polymerizable material 222 isetched after exposure to obliquely directed light as in the case of themethod shown in FIGS. 6A through 6G. In the example of the method shownin FIGS. 7A through 7D, a patterned opaque mask 223 (or alternatively acontact mask) is placed on a photo-polymerizable material 222 which hasbeen placed over the substrate 221. Then obliquely directed light 224and 225 exposes the area surrounding the desired opening and a portionof the area under the mask 223 thereby causing these exposed regions toby polymerized as region 222A leaving the unpolymerized region that wasnot exposed as region 222B. Again, as in FIG. 6D, four sources of lightobliquely angled relative to the surface will typically be necessary,however, two sources at either set of diagonally opposed corners of arectangular mask is sufficient. FIG. 7C shows the result of the exposureafter the mask 223 has been removed. Then the unpolymerized material222B is removed using a conventional etchant which leaves the opening227 as shown in FIG. 7D. The opening 227 in FIG. 7D may be directly usedas the opening to receive separately fabricated blocks. Alternatively,the polymerized material 222A may be used as a mask to etch an openingin the substrate 221. Such an alternative result is shown in FIG. 7Ewhere the polymerized material 222A is left to create a bevel around thetop edge of the opening which now extends into the substrate 221.

FIGS. 8A through 8F show another example of a method according to thepresent invention. A mask material is patterned over a substrate 251 tocreate openings which are thin slots. In one example, the mask materialmay be chrome which forms the patterned layer 252 with openings 253A and253B. FIG. 8C shows an example of such a mask where the openings form arectangle with protrusions from the corners and openings 255 whichresemble pin-hole openings next to these protrusions at the corners. Itwill be appreciated that FIG. 8C is a top view of the patterned masklayer 252 and that these openings in the patterned mask layer 252 exposeportions of the top surface of the substrate 251 which, in oneembodiment, may be glass. The cross-sectional view of FIG. 8A isindicated on FIG. 8C. Through these openings, a wet etch is applied tothe substrate 251 to etch the substrate a small amount, such as 2microns. The resulting etch is shown in FIG. 8B in which the smallopenings 254A and 254B are created in the substrate 251. These openingssurround the chrome island 256 shown from top view in FIG. 8C and fromside cross-sectional view in FIG. 8D. A photoresist is then applied andpatterned over the chrome such that only the center square 256 isexposed as shown in FIG. 8D. The patterned photoresist layer 257 is thenused as a mask to etch the chrome island 256 resulting in the opening258 as shown in FIG. 8E. Then the structure shown in FIG. 8E is etchedagain. In one embodiment, a wet hydrofluoric acid etch is used to etchinto the opening 258 of the substrate 251. This creates the opening 259shown in FIG. 8F. Then the patterned photoresist layer 257 and thechrome layer 252 are removed to produce the final hole.

The various different methods of the present invention will typicallycreate an array of openings on a receiving substrate. These openings arethen filled with a plurality of elements, each of which typicallyinclude at least one function component, such as a pixel driving circuitfor driving a liquid crystal cell in an active matrix liquid crystaldisplay or other display driving elements for other types of displays.Co-pending U.S. patent applications Ser. Nos. 09/251,220 and 09/251,268filed Feb. 16, 1999 by John Stephen Smith and assigned to the sameAssignee of the present invention describe an example of the electricalcircuitry disposed on each element which is to be assembled into anopening. These co-pending applications are hereby incorporated herein byreference. Generally, these elements resemble tapered blocks having atrapezoidal cross-section where the top of the block is wider than thebottom of the block. An example of such a block is shown as block 16 inFIG. 1D. Various improved methods for forming these blocks are describedin co-pending U.S. patent application Ser. No. ______, which was filedconcurrently herewith by John Stephen Smith, Mark Hadley and Jay Tuwhich is assigned to the same Assignee as the present invention andwhich is entitled “Methods for Creating Elements of Predetermined Shapeand Apparatuses Using These Elements” and which is hereby incorporatedherein by reference. In one preferred embodiment, the electricalcircuits are fabricated as described in U.S. patent applications Ser.Nos. 09/251,220 and 09/251,268 in blocks which are fabricated asdescribed by the U.S. Patent Application entitled “Methods for CreatingElements of Predetermined Shape and Apparatuses Using These Elements.”FIGS. 9A through 9D will now be referred to in describing one example ofa method of assembling the blocks into the openings in order to create acompleted assembly.

FIG. 9A shows a generalized flowchart indicating the various processingoperations which are performed to create the completed assembly in whichthe blocks or elements are assembled into the openings in the receivingsubstrate. In processing operation 301, blocks having a predeterminedshape are prepared. In one particular example, an integrated circuit isfabricated into each block and each block is extracted from a firstsubstrate which may be a single crystal semiconductor substrate, such asa monocrystalline silicon wafer. Separately, in step 303, the openingsfor the blocks are prepared in a second substrate. Processing operation303 may employ any of the previously described methods of the presentinvention in order to form openings having a desired shape which isdesigned to match the predetermined shape of the blocks formed inprocessing operation 301. In step 305, the blocks are assembled into theopenings. In one example, the blocks may be assembled by a pick andplace method as described above. In a preferred embodiment of thepresent invention, fluidic self assembly is used to assemble the blocksinto the openings. Fluidic self assembly in one example of the presentinvention may use a slurry of the blocks which are carried in a fluid,such as acetone or water with a surfactant or other types of fluids,including gases or vapors. Agitation and fluid flow to move the blocksover the receiving surface may be used. When a block encounters anopening, it falls into it and is held there. Blocks that do notencounter an opening simply slide off the substrate. Eventually, thesubstrate contains only blocks that are in holes. If any empty holesremain on the substrate, a second dose of block slurry can be depositedon the substrate to fill those holes. Once the desired percentages ofholes has been filled, a binding agent may be added and the slurrysolvent, such as acetone, is evaporated.

In processing operation 307, the assembly is planarized. In one example,the substrate with the blocks is spin-coated with partially polymerizedbenzocyclobutene to a uniform thickness of greater than 2 microns. Thisplanarization layer is then cured. FIG. 9B shows an example of a block,referred to as silicon block 325 having an active device layer 327 atthe top surface of the block 325. The block sits securely in the opening323 in the glass substrate 321. The planarization material is shown inFIG. 9C as material 329 which fills the gaps in the opening 323 and alsocoats the upper surface of the glass substrate 321 and covers the block325 and the active circuit layer 327.

Vias are then etched in the planarization layer and electricalconnections are made to bonding pads on the integrated circuit in theactive circuit layer 327. Processing operation 309 as shown in FIG. 9Amay include other methods for interconnecting the various blocks in thevarious openings along the substrate. In the case of an array of displayelements, metallization is applied into the vias 331 in order to makecontact to bonding pads on the active device layer 327 of the block 325.These patterned metal layers, such as metal lines 333A and 333B, serveto interconnect the blocks electrically. For example, these metal lines(or non-metal conductive lines) may represent a row line for a row ofpixels or may represent a column line for a column of pixels as is wellknown in the art of fabricating active matrix liquid crystal displays.

The Fluidic Self Assembly (FSA) process can be performed in a variety ofconditions, with a variety of fluids. Proper selection of the block andsubstrate surface chemistry as well as the fluid to be used results infaster, higher yielding assemblies with dramatically fewer excess blocksleft on the surface prior to rinsing, inspection, and repair. Thesurface chemistry interaction with the fluid effectively reduces theamount of friction between the blocks and the substrate. The choice ofblock surface chemistry, substrate surface chemistry, and fluid are allusually interrelated. For example, hydrophobic surface chemistries workmuch better with organic fluids than with aqueous solutions. Thetreatment of the surfaces usually, but not necessarily, alters both setsof surfaces so that they are of the same type. For example, both theelements and substrate may be treated to have a hydrophilic surface andthe elements, so treated, may be dispersed in a polar solvent (e.g. H₂0)and then dispensed over the so treated substrate in an FSA process. Inan alternative example, both the elements and the substrate may betreated to have a hydrophobic surface and the elements and substrate, sotreated, may be combined in a solvent (e.g. hexane) which is non-polarin an FSA process.

In the case of the block surface chemistry, any surface treatment thatcleans the surface of the block results in improved FSA's. A surfacetreatment fluid may be in a liquid form, a gas form or a plasma form.The improvement is more significant if the surface treatment leaves adesired, uniform surface chemistry on all of the blocks for a givenassembly. Hydrophilic surface chemistries can be achieved by rinsing theblocks in any oxidizing solution, such as aqueous KMnO₄, H₂SO₄ withH₂O₂, NH₄OH with H₂0₂, or ozonated deionized water or by exposing theblocks to an oxygen plasma. The surface chemistry is more uniform if theblocks can be agitated while being immersed in one of the precedingchemistries. The agitation could be caused by a variety of systems, suchas from a recirculating fluid flow, from a megasonic or ultrasonic bath,or by stirring. Hydrophilic surfaces with good uniformity can beachieved by oxidizing the surfaces and reacting a functional,self-assembled monolayer onto the surface, and then oxidizing thefunctional group in the self-assembled monolayer. For example,octenyltrimethoxysilane could be reacted onto block surfaces cleaned byoxidation with H₂SO₄ and H₂O₂. The alkene group can then be oxidizedinto a hydrophilic functional group by treatment with a mild, aqueousKMnO₄ solution.

Hydrophobic surfaces on blocks can be created by cleaning and oxidizingthe blocks as described above, and then reacting a self-assembledmonolayer onto the surface, such that the hydrocarbon chains of theself-assembled monolayer are topmost at the surface. Typically thecontact angle of water on these hydrophobic surfaces is at least 90degrees. Teflon, which can be deposited or formed on the surfaces of theblocks, will also act to create hydrophobic surfaces on the blocks.Other types of coatings of a hydrophobic nature may be used or afluorine plasma may be used to create hydrophobic surfaces on theblocks.

The substrate surface treatment is analogous to the block surfacetreatment. It is possible to perform fluidic self-assemblies in whichthe block receives one surface treatment, and the substrate receives adifferent surface treatment. For example, the substrate may be exposedto a surface treatment fluid which creates a metal coating (film) on thesurface of the substrate (a hydrophilic surface normally) or a surfacetreatment fluid which is an oxygen plasma (to create a hydrophilicsurface) or a surface treatment fluid which oxidizes a coating (orotherwise creates an oxidized coating) on the substrate while the blocksare exposed to a surface treatment fluid which is dissolved ozone inwater. Alternatively, the same surface treatment fluid (e.g. an oxygenplasma) may be used on both the blocks and the substrate. It is alsopossible to pattern the surface treatment on the substrate, such thatthe surfaces in the bottom of the receptor sites are hydrophilic, andthe rest of the substrate is hydrophobic, for example.

As mentioned above, the choice of fluid for any given FSA depends on thesurface chemistry of the blocks and the substrate. Assemblies processedwith hydrophobic surface chemistries (e.g. the blocks and substrate haveeach been exposed to surface treatment fluid(s) which have createdhydrophobic surfaces on the blocks and the substrates) proceed morerapidly if an organic solvent, such as toluene or hexane, is used as theslurry fluid in the FSA process. Conversely, if the blocks and substrateare hydrophilic (because the blocks and substrate have been exposed tosurface treatment fluid(s) which have created hydrophilic surfaces onthe blocks and the substrate), water or hydrophilic solvents such asacetone (or other polar or water soluble solvents) are more appropriateas the slurry fluid in the FSA process.

A preferred method of surface treatment for the block devices is tooxidize the surface with a dilute aqueous solution containing 0.008%potassium pernanganate, 0.025% sodium periodate, and 0.415% potassiumcarbonate. The block devices are stirred in the oxidizing solution at75° C. for 2 hours. The preferred method for stirring the block devicesin the solution is to separate the block devices from the stirrer by astainless steel sieve material. After 2 hours of exposure to theoxidizing solution, the block devices are collected on the sieve, andrinsed in a 0.3M aqueous sodium bisulfite solution. Then the devices arerinsed in a 0.1M solution of acetic acid. Finally, they are rinsed in DI(deionized) water.

The most preferred method is to oxidize the block devices while theyrecirculate in a solution of 5 to 125 ppm dissolved ozone in DI water.The most preferred ozone concentration is in the range of 50-125 ppmdissolved ozone. The block devices are recirculated for 1 hour, rinsedin DI water, and then transferred to the slurry fluid prior to fluidicself assembly.

The most preferred method for treating a glass or silicon substrate isto place the substrate in a mix of 95 parts concentrated sulfuric acidand 5 parts hydrogen peroxide for 10 minutes. The substrate is thenrinsed in DI water prior to fluidic self assembly.

A preferred treatment for treating plastic substrates (e.g. a flexibleplastic substrate) is to expose them to gaseous ozone for 5 minutes. Themost preferred method for treating a plastic substrate is to expose thesubstrate to an oxygen plasma for 1 minute prior to fluidic selfassembly.

Besides surface interaction, the optimal fluids for FSA have lowviscosity and can be used safely. It is possible to add reagents to thefluid to improve the FSA process. For example, surfactants or certainwater soluble polymers can be added to water to reduce theblock-substrate interaction, thereby reducing the number of excessblocks left on the substrate at the end of an assembly. If a polymer isused, it is desirable that the polymer serve as a lubricant whiledissolved. Preferred polymers would consist of water soluble polymerssuch as Union Carbide Polyox (polyethylene glycol) or DuPont Elvanol(polyvinyl alcohol). If a surfactant is used, it is preferable to use anon-ionic surfactant so that the circuitry is not damaged by counterionsin the surfactant. The surfactants normally have a molecular form whichincludes a hydrophobic portion and a hydrophilic portion; often, thenon-ionic surfactant will include a hydrophilic portion which is anethylene oxide oligomer. In a preferred method, a non-ionic surfactantsuch as Union Carbide MinFoam 1X or Triton 190 or DuPont Zonyl FS-300 isused in water to perform fluidic self assembly of blocks which have beensurface treated with aqueous KMnO₄ (or ozonated water) on a glasssubstrate that was oxidized with H₂SO₄ and H₂O₂. In this case, the waterand surfactant and the blocks form the slurry for the FSA process, andthe slurry is dispensed onto the pretreated substrate. Typically, thesubstrate is immersed in the FSA fluid (e.g. water in the immediatelypreceding example) which is the same as the fluid used to create theslurry having the blocks, and the slurry is added to the substrate whileit is immersed in the FSA fluid. The substrate may be immersed inexactly the same fluid and a surfactant as the fluid and surfactantwhich make up the slurry.

Once the blocks and the substrate are prepared in the desired manner(e.g. the desired surface treatments have been completed), and theappropriate carrier fluid is selected, the blocks can be deposited ontothe substrate in a number of ways. They can flow down an inclined tubecontaining the fluid so that they fall through the FSA fluid and ontothe substrate. One or a plurality of these tubes can be used to depositthe blocks onto the substrate. Also, the tube or tubes can be movedacross the substrate such that the entire substrate can be covered withblock slurry prior to or during assembly. In another embodiment, theblocks could be carried through a tube or a number of tubes by a fluidflow that is either laminar or turbulent. The flow(s) could effectivelyspray the block slurry over the substrate to cover a selected portion ofor the entire substrate. The aforementioned tubes could be circular,fan-shaped, or have a multitude of ports.

The fluidic self assembly process can be accomplished in a variety ofmethods. The blocks can be moved across the substrate surface in anumber of ways, including forced fluid flow, suction, gravity, magneticfields if the blocks have magnetic characteristics, or any combinationof these driving forces. Forced fluid flow can drive the blocks across atilted or horizontal substrate either by providing a uniform flow overthe surface, or by using a very localized flow that can be directed inany desired manner. A magnetic field applied to magnetized blocks coulddraw the blocks into the receptor sites. Suction could be applied toholes located in the bottom of the receptor sites that go through thesubstrate to a vacuum source on the other side of the substrate. Gravityis used by tilting the substrate from horizontal to an angle not greaterthan 55 degrees. The blocks then slide down the substrate under theforce of gravity. In a preferred embodiment, the tilted substrate isvibrated to drive the blocks down the substrate. The vibration frequencyranges from 50 Hz to 10,000 Hz, and can have a square, sine, sawtooth,or any other waveform. The direction of the vibration is in oneembodiment transverse to the direction of the block slurry flow down thetilted substrate. In some instances it may be desirable to havecomponents of the vibration in the direction of the block flow down thesubstrate, and in the direction normal to the substrate.

Once the blocks are moving across the substrate, the fluidic selfassembly can proceed by either allowing all of the excess blocks (blocksthat do not fill a receptor site) to move completely off of thesubstrate, or by forcing excess blocks to move off of the substrate. Theexcess blocks can be driven off of the substrate with fluid flow overthe substrate, by altering the conditions of the vibration applied tothe substrate during the assembly, by increasing the angle ofinclination of the substrate, by suctioning off blocks, or by anycombination of these methods.

The fluidic self-assembly process can be accelerated in a number of waysin addition to proper selection of the process parameters listed above.One method for speeding up the FSA process is to deposit blocksregularly or uniformly over the entire surface. This deposition processcould result in a uniformly dense layer of blocks across the surface.This could be accomplished by spraying the block slurry across thesubstrate with one or more deposition nozzles. If desirable, thenozzle(s) could be designed to sweep across the surface to achieve moreuniform coverage. Alternatively, the blocks could be deposited inselected areas of the substrate. These blocks could be placed by one ormore fixed or movable deposition nozzles that deliver the blocks withthe assistance of some combination of fluid flow, gravity, andvibrational impulse. Placing the blocks uniformly or regularly over thesubstrate surface accelerates the overall FSA process because less timeis required for the blocks to move over the entire substrate. Forexample, if 10 rows of blocks are deposited regularly over the substratesurface, the blocks will only have to move one-tenth the distance acrossthe substrate as compared to the case in which just one row of blocks isplaced at the top of the substrate. Once a sufficient number of blockshas covered the areas of the substrate containing the receptor sites,such that the desired number of the receptor sites are filled, theexcess blocks can be forced off of the substrate. FIGS. 11A and 11B showtwo examples of nozzle heads which include at least one nozzle. Nozzlehead 450 includes three nozzles 451, 452 and 543. Each nozzle 451, 452and 453 may be coupled to receive the same fluid (e.g. a slurry withblocks) or different fluids (e.g. one nozzle ejects a slurry withblocks, one nozzle ejects “helper” blocks (described below) in a fluid,and another nozzle may create a vacuum to be used to remove excessblocks after depositing blocks and allowing them to settle/self-assembleinto openings). Nozzle head 456 includes many nozzles 457 disposed alonga row; these many nozzles are designed to eject a fluid (e.g. a slurrywith blocks and/or helper blocks) or to draw a vacuum. Several nozzleheads 456 may be disposed above a substrate to uniformly andconcurrently deposit blocks onto the substrate.

The excess blocks can be removed from the substrate by the methodslisted above. The excess block clearing process can be accelerated withthe addition of components designed to push blocks off of the substrate.Any combination of a number of different components could accomplishthis task. One component that can increase clearing is a wiper bladethat moves across the substrate. Blocks that are in receptor sties willbe unaffected, but blocks on the surface will be swept away by the wiperblade. Alternatively, a brush could be used in place of or in additionto the wiper blade. The components that clear excess blocks from thesurface could be one or more large items, relative to the size of theblocks, that move down the substrate with the blocks, pushing blocksdown and off the substrate as they move. These items may be referred toas helper blocks. Because these items are normally significantly largerthan the blocks, gravity will drive them down the substrate faster thanthe blocks, and they will be able to push a large number of the blocksoff of the substrate as they move down. These relatively large itemscould be glass, plastic, or metal balls, cylinders, or rectangularsolids. More preferably, these items could have the same approximateshape as the blocks (but larger in size), or they could be shaped piecesof material that are designed to contact the substrate only where thereare no receptor sites. Most preferably, these helper blocks could berectangular pieces made of magnetic stainless steel. After removing theexcess blocks from the surface, these items could be recovered andreadily separated from the excess blocks by sieving or some otherparticle separation method or separated with a magnetic field in thecase where the helper blocks are magnetic (e.g. the helper blocks arecomprised of magnetic material).

After the excess blocks have been removed, the substrate can beinspected for faults such as empty holes or blocks that have not seatedproperly in their receptor sites. Empty sites can be filled by placing asmall number of blocks in a slurry form and depositing this slurry on orabove the empty site, and forcing or allowing the blocks to fill theempty site(s) by means analogous to those used to perform the assembly.Empty sites can also be repaired by a pick-and-place process, in whichan individual block is placed in an individual receptor site. A receptorsite with an improperly seated block can be repaired by removing theblock with either suction, fluid flow, or mechanical means, and thenfilling the now empty receptor site as described above. Alternatively,blocks that are tilted or rotated in their receptor site could berepaired after the assembly is complete with a hot press process.

Once all desired repairs have been made, the blocks may be bonded intotheir receptor sites with an organic or polymeric agent that serves asan adhesive in this application. The bonding agent could be dissolvedinto the original FSA fluid prior to the start of the assembly, or itcould be added any time later during the assembly, assuming that thebonding agent is compatible with the fluid used for the assembly. If thebonding agent is incompatible with the fluid used for the assembly, afluid displacement process can be used at any time after the start ofthe assembly to replace the first fluid with a second fluid which iscompatible with the bonding agent. In one example, acetone is used asthe FSA fluid, and a water soluble polymer is used as the bonding agent.After completion of the inspection and repair process, water is added tothe system and acetone is removed at approximately the same rate, untilthere is a sufficient percentage of water in the resulting water/acetonemix such that the bonding agent is soluble in the mix. In a differentexample, the FSA is performed in toluene containing benzocyclobuteneoligomers which serves as a bonding agent. In another example, the FSAis performed in basic water that contains surfactant and a water solublepolymer that serves as the bonding agent. Alternatively, the FSA can beperformed in water containing surfactant, and then a water solublebonding agent dissolved in water can be added to the water/surfactantmixture. Typically the completed assembly is left immersed in thebonding solution for 5-30 minutes to allow the bonding agent to diffusearound the blocks in the receptor sites. At this time, if the substratewere tilted it is preferable to reduce or eliminate the angle ofinclination, and, in some cases, to apply a low amplitude vibration tothe substrate while the angle of inclination of the substrate is beingdecreased.

After the filled substrate has remained immersed in the bonding solutionfor the desired length of time, the substrate is either lifted out ofthe solution, or more preferably, the solution is drained away orevaporated from the substrate. Then the substrate is allowed to dry,either by free or forced convection. During the drying process, it isbeneficial to tilt the substrate slightly, so that excess fluid does notpool and dry in the array of blocks.

Once the substrate is dry, the fluidic self assembly process iscomplete. At this time, if necessary, repair of blocks that are tiltedin their receptor sites can be accomplished with the use of heat andmechanical pressure in a number of different ways. The substrate can beheated to a temperature that softens the bonding agent, and thenpressure can be applied either locally with a point source, moreglobally with a roller apparatus, or globally with weight or other formof applied pressure. In this step it is important that the surfacepressed against the filled substrate will not stick to the blocks in thereceptor sites or to the substrate. In one example, Solutia Scripset 550was used as the bonding agent, the substrate was heated to 120° C., andthen pressed between perfluoroalkoxy polymer films with approximately500 psi for 1 minute. The substrate is then cooled while under pressure.The pressure is released and the perfluoroalkoxy films were removed. Inanother example with the same bonding agent, a Teflon roller, made outof Teflon tubing placed over a steel rod, was rolled across thesubstrate after it was heated to 120° C. Both of these processes reducedthe number of tilted blocks that remained after the completion of theFSA.

After the completion of the FSA, and the press repair if desired, theresidual bonding agent that remains on the surface of the substrate canbe removed with an oxygen plasma descum without damaging the bonding ofthe blocks in their receptor sites. At this point, the substrate isready for planarization and the rest of the down stream processesrequired to electrically interconnect the blocks and construct anelectrical apparatus.

FIG. 10 shows a flowchart of an exemplary method of the invention whichincludes the pretreatment of the blocks and the substrate and thebonding of blocks into openings as described above. This FIG. 10 alsooptionally uses helper blocks to facilitate movement of the blocksacross the substrate during the FSA process. Operations 401 and 403include the pretreatment of the surfaces of the blocks and thesubstrates. Alternatively the fluid used in operation 405 may be used topretreat the blocks' surfaces. In operations 407 and 409 the FSA processoccurs, and excess blocks (and helper blocks if used) are removed inoperation 411. Then the blocks are bonded into the openings (after useof a roller as described above) in operation 413. A repair process maybe used as described above and then the substrate is processed infurther down stream processes (e.g. planarization and electricalinterconnection) in order to create a functional device, such as anactive matrix flat panel display.

FIGS. 9E, 9F, 9G, 9H and 9I show the result of an FSA process whichfills an opening created using a method according to the processillustrated in FIGS. 3A-3G. FIG. 9E begins with the opening 351 in aglass substrate 350. A block (shown in this case as a silicon Nanoblock353, where Nanoblock is a trademark of Alien Technology, Inc.) isassembled through an FSA process (e.g. the method of FIG. 10) into theopening 351 as shown in FIG. 9F. The top portion of block 353 includesthe functional component (in this case MOS circuitry, such as CMOS pixeldrivers and electrode(s)) for the block. Then, as shown in FIG. 9G, aplanarizing layer 356 is applied. The planarizing layer may be appliedafter a bonding solution is used to bond the block to the opening. Apatterned metal (or other conductive material) layer 357 is then createdto electrically interconnect the block's functional component to otherblocks or to other functional components. FIG. 91 shows an electronmicrograph of a block 353 in a substrate 350 after electricalinterconnects 357 a and 357 b have been applied. Normally, many suchblocks may be formed in a matrix to create, for example, the backplaneof an active matrix flat panel display, such as an active matrix liquidcrystal display.

An exemplary method according to another aspect of the invention willnow be described in conjunction with FIGS. 12A and 12B. FIG. 12A showsan assembly 501 of a substrate 503 with a reflective layer 507 and anablatable layer 505. The substrate 503 may be a glass layer or a plasticlayer which is flexible. The reflective layer 507 may be an aluminumfoil layer which is also flexible, and the ablatable layer 505 may be anorganic polymer or other substances which may be removed (e.g. byevaporation through exposure to selectively located heat). The ablatablelayer 505 is exposed at desired locations to a laser beam 509 whichremoves the ablatable material at the exposed portions, thereby creatingthe opening shown in FIG. 12B. The opening is created to the point atwhich the reflective surface 510 of the foil is reached. Thus, theablation process stops automatically at the reflective surface 510. Thiswill produce uniformly deep openings when the ablatable layer has auniform height across the surface of the foil. The opening may then beused as described above in an FSA process.

An exemplary method according to another aspect of the invention willnow be described in conjunction with FIGS. 13A and 13B. A completelydifferent approach to making block receptor sites on a glass substrateis to form the holes in an organic layer coating a glass substrate. Thisoffers many advantages over etching holes directly into the glass. Thereceptor site fabrication process may be faster and easier on an organiclayer than on glass. It will also yield receptor sites that are betterin the sense that they more accurately match the size and shape of thenanoblocks. FIG. 13A shows an assembly 550 having an organic layer 553,which may be thin relative to the glass layer 551. The opening is thenformed to produce the structure shown in FIG. 13B.

There are several methods that may be used to make block receptor sites.The choice of method depends in part on the material to be used as theorganic layer on the glass. If the organic material is an amorphous orsemicrystalline polymer, the receptor sites may be embossed into thepolymer material with a mold that matches the block size and pitch forthe device being produced (e.g. an active matrix LCD). In this case, itmay be preferable to adjust the mold to take into account thedifferences in thermal coefficient of expansion between the polymer andthe mold material.

Embossing is just one method of forming the receptor sites in apolymeric coating on the glass. The coating may alternatively beinjection molded onto the glass substrate during the coating process.Alternatively, the receptor sites could be formed in the polymer bysolvent casting a polymer solution onto a receptor site mold. Thesolvent cast sheet could then be laminated or transferred to the glasssubstrate.

It is also possible to form the receptor sites in a thin film of eitherthermoset plastic or crosslinkable organic material on the glasssubstrate. The receptor sites are formed by placing the liquid organicstarting material on the mold. It is preferable to treat the mold with arelease coating, such as an oil, a fluorinated coating, or a low-surfaceenergy self-assembled monolayer coating, or one of these materialscombined with a metal layer that separates readily from these coatings,such as silver. The glass substrate is then pressed on top of the liquidorganic material, such that the liquid flows around all of the featuresof the mold, and any bubbles in the liquid are removed. Theglass/organic/mold stack is then exposed to sufficient heat or UV light,if necessary, for a sufficient time to cure the liquid organic materialinto a crosslinked solid material. The mold is then separated from theorganic film on the glass.

It is also possible to pattern the material without a mechanical mold byusing light energy. There are two techniques to accomplish this. First,standard photolithography techniques could be used on a photopatternablematerial to expose and develop away the volume of material in thereceptor site. In this case, the photopatternable material serves as thesubstrate material. Alternatively, a mask layer could be used on top ofthe organic material, such that the organic material could be etchedwith a plasma etch system. This method would apply to a larger class oforganic substrate materials because the organic material does not needto be photopatternable. It is also possible to form the receptor sitesin the organic layer by using a laser drilling or laser ablationtechnique as described above in conjunction with FIGS. 12A and 12B. Thismethod is advantageous because it will work on a large class of organicmaterials, and does not require a photolithography step. This method canalso be used on a plastic substrate on a metal foil. The process caneither be tuned to etch down to a particular depth in the plastic or aplastic-on-foil laminate structure can be used to create an etch stop.Preferably, the plastic film thickness can be the same as the desireddepth of the receptor site, such that in the laser ablation process themetal foil serves as an etch stop as described above.

While the foregoing description has provided examples of the presentinvention, it will be apparent that various modifications may be madewithin the spirit and scope of the invention which is limited only bythe following claims. For example, the order of the processingoperations may be modified and the same or similar result achieved inthe resulting structure.

1. A method of assembling a structure on a substrate, said method comprising: etching said substrate through a first patterned mask; etching said substrate through a second patterned mask to create a plurality of openings in said substrate; dispensing a slurry over said substrate, said slurry comprising a fluid and a plurality of shaped blocks, wherein at least one of said shaped blocks is disposed into one of said plurality of openings.
 2. A method as in claim 1 wherein each of said shaped blocks comprises an electrical component.
 3. A method as in claim 2 wherein at least some of said shaped blocks are interconnected electrically.
 4. A method as in claim 2 wherein each of said shaped blocks is fabricated before being added to said slurry and wherein said electrical component is at least one of (a) a transistor; (b) a capacitor; (c) a resistor; (d) an inductor; (e) an electrode; and (f) a diode.
 5. A method as in claim 1 wherein each of said openings comprises a beveled edge at a top surface of said substrate and wherein for each of said openings said opening is larger near said top surface than near a bottom of said opening.
 6. A method as in claim 5 wherein said slurry is dispensed over said substrate at a rate which is substantially a uniform flow and allows each of said shaped blocks to self align into one of said openings.
 7. A method as in claim 1 wherein said etching through said first patterned mask produces an edge under said first patterned mask and wherein said method further comprises: exposing said edge; etching said edge before said etching through said second patterned mask, said etching said edge producing a beveled top edge for each of said openings.
 8. A method as in claim 1 wherein said second patterned mask comprises a portion which extends into a first etched region of said substrate which was etched by said etching through said first patterned mask.
 9. A method as in claim 8 wherein said second patterned mask is formed by: applying a second mask material over said substrate and into said first etched region and over a second etched region which was etched by said etching through said first patterned mask; exposing said second etched region by etching a portion of said second mask material.
 10. A receiving substrate which is designed to receive an element fabricated in a first substrate, said receiving substrate comprising: a receptor region having an opening in said receiving substrate, said opening comprising a beveled edge at a top surface of the receiving substrate.
 11. A receiving substrate as in claim 10 wherein said opening comprises a bottom surface formed in said receiving substrate, said bottom surface being substantially flat.
 12. A method for creating an opening in a layer, said opening for receiving an element which is placed into said opening, said method comprising: forming a first layer on a substrate; depositing a second layer over said first layer; ablating selectively said second layer at at least one desired region to create an opening in said second layer at said at least one desired region, wherein said ablating stops automatically at said first layer.
 13. A method as in claim 12 wherein said first layer comprises a reflective layer and said ablating comprises exposing said second layer to radiation from a laser.
 14. A method as in claim 13 wherein said first layer acts as an automatic ablation stop.
 15. A method as in claim 12 further comprising, after said opening is created, a method for assembling a structure onto said substrate, wherein a plurality of openings, including said opening, are created in said second layer, said method for assembling comprising: dispensing a slurry over said second layer, said slurry comprising a fluid and a first plurality of elements each of which is designed to mate with a corresponding one of said plurality of openings and each of which comprises a functional element.
 16. A method as in claim 15 wherein said slurry further comprises a second plurality of elements which are not designed to mate with openings of said plurality of openings.
 17. A method as in claim 16 wherein said second plurality of elements facilitate movement of said first plurality of elements over said second layer and do not include any functional elements.
 18. A method as in claim 15 wherein said slurry further comprises a bonding agent which is dissolved into said fluid and wherein said method of assembling further comprises: evaporating said fluid after each of said first plurality of elements has mated with said corresponding one of said plurality of openings, wherein said bonding agent bonds each of said first plurality of elements to said corresponding one of said plurality of openings. 